Powered by AI
Copilot
Writing electron configurations involves understanding the arrangement of electrons in an atom’s orbitals. Here’s a
step-by-step guide to the logic behind electron configurations:
Basic Principles
1. Aufbau Principle: Electrons fill orbitals starting from the lowest energy level to the highest. This means
they fill the 1s orbital before the 2s orbital, and so on.
2. Pauli Exclusion Principle: Each orbital can hold a maximum of two electrons with opposite spins.
3. Hund’s Rule: Electrons will fill degenerate orbitals (orbitals of the same energy) singly before pairing up.
This minimizes electron-electron repulsion.
Steps to Write Electron Configurations
1. Identify the Atomic Number: This tells you the number of electrons in a neutral atom.
2. Follow the Order of Orbitals: Use the periodic table or an orbital filling diagram to determine the order in
which orbitals are filled. The order is generally:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.
3. Fill the Orbitals: Distribute the electrons among the orbitals following the Aufbau principle, Pauli
exclusion principle, and Hund’s rule.
Example: Writing the Electron Configuration for Carbon (Atomic Number 6)
1. Determine the Number of Electrons: Carbon has 6 electrons.
2. Fill the Orbitals:
1s²: The first two electrons go into the 1s orbital.
2s²: The next two electrons go into the 2s orbital.
2p²: The remaining two electrons go into the 2p orbital.
So, the electron configuration for carbon is 1s² 2s² 2p².
Example: Writing the Electron Configuration for Iron (Atomic Number 26)
1. Determine the Number of Electrons: Iron has 26 electrons.
2. Fill the Orbitals:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶.
So, the electron configuration for iron is [Ar] 4s² 3d⁶ (using the noble gas shorthand notation).
Using the Periodic Table
The periodic table is a helpful tool for writing electron configurations:
Periods: Indicate the principal energy levels (n).
Blocks: Indicate the type of orbital being filled (s, p, d, f).
Summary
s-block: Groups 1-2 and Helium.
p-block: Groups 13-18.
d-block: Transition metals (Groups 3-12).
f-block: Lanthanides and actinides.
By following these principles and steps, you can write the electron configuration for any element.
Would you like to practice writing electron configurations for specific elements or need more examples?
